Owing to the body-mind duality myth, that is. This logical argument chain makes sense insofar as people could perform as black and then be black, much in line with TERF anti-trans ideologies. Yet, this gets rid of the complexities of the process and accumulated lived experiences, basically strawmaning "I want to be a girl" or "I must abort" as if they were trends.
Now, even if instrumentally acknowledging it as an aesthetic-identity privilege "entitlement" of some white people who transition (though note most are vulnerable and face many barriers, institutional, economical, and familiar, from an already poor household), the logic disregards the impacts of trends and long term, only focusing on the immediate after. It fearmongs in an infantilising about the "correct (hegemonic) development" for an adolescent, but most importantly, it decenters the loss of privilege and the abuse and backlash faced from following this process, highligting the statist objectivist biases that engendered binaryist stereotypes.
One can't simply impersonate and live someone else's life. Fantasy can approach us to it, and be very vivid at doing so, but the approach will be a momentary peak of attention that is not usually maintained as it is not continuously lived, embodied.
Identity might not be a right, sure, but oftentimes, but the right-wind reframing displaces the debate here... we are not visiting Jakarta or the North Pole as exotic tourists, we are commiting to a change of reality because over multiple years of questioning and trying changes, we've decided it's the way to go. This is not about white people having a right to racialised bodies like fast clothing or food, this is about acknoweldging other ways of living as valid through an ethics of care that decenters the falsely "efficient" white male default. It's about saying yes to diverse ways of living that don't exploit the world, because some "being" blind, asexual, autistic, indigenous, and why not, fat, is not somethign that one usually "choses", and thereby, without relying on naturalistic fallacies but on a decentering anti-monopoly axiology, we should provide safe spaces for these to flourish.